Loaded double-folded slot antenna



Feb. 20, 1962 Filed March 29, 1960 G. A. SCHARP LOADED DOUBLE-FOLDED SLOT ANTENNA 6 Sheets-Sheet 1 INVENTOR.

GLENN A. SCHARP gwfim if ATIORNE Ys.

b- 1962 G. A. SCHARP 3,022,505

LOADED DOUBLE-FOLDED SLOT ANTENNA Filed March 29, 1960 6 Sheets-Sheet 2 v Bandwidth L/w wf/wd (wavjfe ngths) (iii s (wavef xfgths) for Power Rachated Dumbbell diameter 5" FIG. 3

IN VEN TOR.

ATTORNEYS.

HALF RESISTANCE (R) Feb. 20, 1962 G. A. SCHARP 3,022,505

LOADED DOUBLE-FOLDED SLOT ANTENNA Filed March 29, 1960 6 Sheets-Sheet 3 w /w 1/6 s=9/s L=20.5" L/W=8.2

(D 2 I Q 2 DJ Q E 2 '6 m y I40 I I 200 220 240 260 280 300 320 FREQUENCY (Mo) f 223 Me L 0.378 3 BAN DWIDTH 28.5% POWER 3 RADIATED 2 I V I80 200 220 240 260 280 309 FREQUENCY (Mc) INVENTOR.

ATTORNEYS.

Feb. 20, 1962 e. A. SCHARP 3,022,505

LOADED DOUBLE-FOLDED SLOT ANTENNA Filed March 29, 1960 e Sheets-Sheet 4 4 W W /2 I u COAXIAL TRANSMISSION GROUND PLANE LINE FIG. 7

INVENTOR.

GLENN A. SCHARP Feb. 20, 1962 Filed March 29, 1960 G. A. SCHARP 3,022,505

LOADED 00013112401020 $1.01: ANTENNA 6 Sheets-Sheet 5 f d S02 Roz/z L02 07: 23: 2:32:

(wavelengths) (ohms) (wavelengths) Radiated L/W s FIG.8

INVENTOR.

GLENN A. SCHARP ATTORNEYS.

HALF-RESISTANCE (R) AND HALF-REACTANCE (X) IN OHMS Feb. 20, 1962 G. A. SCHARP 3,022,505

. LOADED DOUBLE-FOLDED SLOT ANTENNA Filed March 29, 1960 6 Sheets-Sheet 6 W /W =l/4 S=I3ll2 L=20" L/W=8 8O FREQUENCY (MC) 4 FIG.9

BAN DWIDTH =38.5%

VSWR

200 220 240 260 280 300 320 FREQUENCY (MC) FIG. /0

INVENTOR. GLENN A. SCHARP fimifw ATTORNEYS.

United States Patent Uihce 3,022,505 Patented Feb. 20, .1962

LOADED DOUBLE-FOLDED SLOT ANTENNA Glenn A. Scharp, Norco, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Mar. 29, 1960, Ser. No. 18,453 4 Claims. (Cl. 343767) (Granted under Title 35, US. Code (1952), sec. 266) The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to slot antennas and more particularly to a new and improved folded slot antenna and a new and improved loaded double-folded slot antenna.

The purpose of the antenna of the present invention is to efiiciently radiate or receive electromagnetic energy at a frequency whose wavelength is greater than twice the antenna length while presenting a broad choice of desirable impedance to the generator or receiver. This invention is also related to copending application for Double-Folded Slot Antenna by Glenn A. Scharp, Serial No. 18,454, filed March 29', 1960, now abandoned.

The old method of radiation or reception was accomplished by means of a simple slot antenna. The simple slot had a narrower bandwidth and occupied more space than the antenna of this invention.

The present invention provides a doubleolded slot antenna which is similar, in part, to the old simple slot but which has two ungrounded parallel plates placed inside of and flush with the slot surface. This antenna is also an improvement over the folded slot antenna disclosed in U.S. Patent 2,751,589.

The present invention also provides a loaded doublefolded slot antenna which is similar, in part, to an old dumbbell-loaded slot but which has two ungrounded parallel plates placed inside of and flush with the slot surface. This antenna is an improvement over the dumbbell loaded slot antenna disclosed in US. Patent 2,507,528. The loaded double-folded slot antenna of this invention has a greater bandwidth, shorter length and a wide choice of feedpoint impedances obtained by varying the widths of the center plates; it also has the ability to feed half of it over a ground plane if desired.

it is an object of the invention, therefore to provide a new and improved loaded double-folded slot antenna.

It is another object of the invention to provide a loaded double-folded slot antenna which operates at a frequency whose wavelength is more than twice the antenna length.

Still another object of the invention is to provide a double-folded slot antenna.

A further object of the invention is to provide a loaded folded slot antenna which can be bisected and half of it fed over a ground plane.

It is a still further object of the inventionto provide a double-folded slot antenna which operates at a frequency whose wavelength is more than twice the antenna length.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIGURE 1 is a plan view of a preferred embodiment of the invention, showing a dumbbell-loaded double- FIGURE 4 is a graph showing the variation of impedance (resistance and reactance) with frequency for a select dumbbell-loaded double-folded slot antenna of the present invention;

FlGURE 5 is a curve showing the variation of VSWR (voltage standing wave ratio) with frequency for a select dumbbell-loaded double-folded slot antenna of the present invention;

FIGURE 6 is a plan view of another embodiment of the present invention, showing a double-folded slot antenna;

FIGURE 7 shows a half double-folded slot antenna over a ground plane, as used for impedance measuring;

FIGURE 8 is a table showing statistics for the antenna of FIGURE 6;

. FIGURE 9 is a graph showing the variation of impedance (resistance and reactance) with frequency for a select double-folded slot antenna of the present invention; and

FIGURE 10 is a curve showing the variation of VSWR (voltage standing wave ratio) with frequency for a select double-folded slot antenna of the present invention.

The loaded double-folded slot antenna of the present invention consists of a slot 10 in a conducting sheet 12 and loaded at opposite ends by means of circular apertures 14 and 16, the resulting slot being in the shape of a dumbbell. Two ungrounded parallel plates 18 and 20 are positioned inside and flush with the slot surface. The two metal strips 18 and 26' are supported in place in the plane of slot 16 and circular apertures 14 and 16 by a dielectric material 22, such as polystyrene or Teflon for example. Power is fed through a balanced transmission line, not shown, to adjacent feedpoints 24 and 216 provided on parallel plates 18 and 2 respectively, as shown in FIGURE 1. This antenna can be bisected and I fed with a coaxial cable through a ground plane, if desired.

Impedance curves have been made for this antenna for chosen values of W;/ W and S, where W is the width of the folded (outside) element, W is the width of the driven (center) element, and S is the distance between the centers of the folded and driven elements, as indicated on the drawings. L is overall length of slot 10, W is the width of the slot, and L is the length of the parallel plates 18 and 20.

The impedance measuring method used for the dumbbell-loaded double-folded slot antenna was the ha antenna-over-ground-plaue system shown in FIGURE 2. All impedances are one-half the impedances for a complete antenna in free space. The table of FIGURE 3 shows limitations that are present on S and W /W The slot length L and the dumbbell diameter are given with the table along with the ratio of slot length to slot width L/ W. For the antenna used by way of example, slot length L=20.5 inches and the dumbbell diameter=5 inches. Some important conclusions drawn from this table for a dumbbell-loaded double-folded slot antenna are:

Increasing value of W /W decreases the second resonant frequency (f slightly;

The size of S has no eifect on the second resonant freq y (fez);

A general reduction in the second resonant radiation resistance (R occurs when increasing W /W and The range of bandwidth for power radiated (voltage standing wave ratio VSWR=1.9) for Z =R line feeding the slot is from 10% to 22%, Z being the impedance at resonant frequency.

The reactance (X) remained capacitive throughout the desired frequency range (below 0.500%) for values of Wf/Wd greater than 0.17, as shown by the reactance component of the impedance curves of FIGURE 4. In the 3 table of FIGURE 3, the bandwidth for 90% power radiated was determined by using a transmission line feed impedance of Z R However, by using a compromising value of impedance (2 between the first resonant radiation resistance (R and the second resonant radiation resistance (R a bandwidth of 24% can be obtained. By choosing the operating frequency in the middie of the band, the bandwidth shown in FIGURE 5 can of W W =1/ 6, S-=9/ 8 inches, L=20.5 inchesand L/W=8.2 were used. With dumbbell loading of adoubie -folded slot antenna wavelength shortening to 0.38).

can be obtained at 28.5% bandwidth. 7 V

The'double-folded slot antenna of the present inven tion consists of a slot 30 in a conducting sheet 32 with,

two ungrounded parallel plates 34 and 36 positioned inside, and flush with the slot surface. The two metal strips 34 and 36 are supported in place in the plane of slot 30 by a dielectric material 38, such as polystyrene or 'centers of the folded and driven elements, as indicated on the drawings. L is the length of the slot 30, W is the width of the slot and L is the length of the parallel plates 34 and 36.

Theimpedance measuring method used for the double-folded slot antenna was the half-antenna-overegroundplane system shown in FIGURE 7. All impedances are one-half the impedances for a complete antenna in free space. The table of FIGURE 8 shows the limitations that are present on S and W /W The slot length L and the ratio of slot length to the slot width L/ W are given with the table. For the embodiment given by way of example, slot length L=20 inches and the ratio of slot length to slot width L/W=-8.' Some important conclusion drawn from this table for a double-folded slot an tenna are:

W lW and S have little eifect on the second resonant frequency (fez);

As S is reduced the second resonant radiation resistance 7 (R increases slightly; 7 V

The second resonant radiation resistance (R decreases with increasing W /W and t The range of bandwidth for 90% power radiated (voltage standing wave ratio VSWR=1.9) for Z =R line feeding the slot is' from 14% to 27%; Z being the impedance at resonant frequency. 7

The reactance (X) component of the impedance curves, for double-folded; slots in general, crosses the zero axis twice between 250A (148 me.) and 0.500% (296 me), which is desirable for broad-band applicationsyand example is shown in FIGURE 9. In the table of FIGURE '8, the bandwidth for 90% power radiated was determined using a transmission line feed impedance of Z =R However, by using a compromising value of impedance (Z between the first resonant radiation resistance (R and the second'resonant radiation resistance (R bandwidths of 34.5% to 38.5% can be obtained. The curve be obtained. For the curves'of FIGURES 4 and 5. values I 4 e of FIGURE 10 is shown for a bandwidth of 38.5%. By choosing the operating frequency in the middle of the band, bandwidths from 34.5% to that shown in FIGURE 10 can be obtained. For the'curves of FIGURES 9 and 10 values of W /W =l/4, 5:13/ 12 inches, 11:20 inches and L/W=8 were used. V

A double-folded slot, as in the present invention, can replace a simple slot in many applications and will be particnlarly advantageous where shorter wave length (040A to 0.45M and higher bandwidth (34.5% to 38.5%) are desired. t

Obviously many modifications and variations-of the present invention are possible in the lightof the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A broadband double-folded slot antenna comprising a conducting plane having a rectangular slot therein, two flat ungrounded and spaced-apart parallel rectangular strips of conduct-ing material slightly shorter than the length of said slot symmetrically disposed sdie-by-side Within and lying in the plane of said slot, said parallel strips being supported within and parallel to the longer sides of the rectangular slot by a'dielectric material of suitable dielectric constant, two feedpoints symmetrically positioned on said flat parallel strips for connection with suitable transmission line, 'said antenna being resonant and operable to efiiciently receive and radiate electro magnetic energy at a frequency Whose wavelength is more than twice the antenna length.

2. An antenna as in claim 1 wherein said rectangular slot has a circular aperture at each end thereof thus giving said slot a dumbell configuration.

3. A broadband double-folded slot antenna comprising a plane of conducting material having a rectangular slot therein, two flat'ungrounded parallel strips of con ducting material slightly shorter than the length of said rectangular slot symmetrically disposed side-by-side inside of and lying in the plane of and parallel to the longer sides of said rectangular slot, two feedpoints' symmetrically positioned on said flat parallel strips for connection with suitable transmission line, said antenna being resonant and operable to efliciently receive and radiate electromagnetic energy at a frequency whose wavelength is more than twice the antenna length.

4. An antenna as in claim 3 wherein said rectangular slot has a circular aperture at each end thereof thus giving said slot' a dumbbell configuration.

References Cited in the file of this patent UNITED STATES PATENTS 2,507,528 Kandoian May 16, 1950 2,946,055 Fafiick 'July 19, 1960 2,972,147 Wilkinson Feb. 14, 1961 FOREIGN PATENTS I 655,045 Great Britain July 11, 1951 1,012,833 France July 17, 1952 OTHER REFERENCES 7 Slot-Antenna Array for Missiles and Aircraft Elec- V tronics, February 27, 1959, pages 5657 relied on. 

